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Sonochemical synthesis of HgSe nanoparticles: Effect of metal salt, reaction time and reductant agent
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JIEC-1774; No. of Pages 6 Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Sonochemical synthesis of HgSe nanoparticles: Effect of metal salt, reaction time and reductant agent Mahdiyeh Esmaeili-Zare a, Masoud Salavati-Niasari a,*, Azam Sobhani b a b
Institute of Nano Science and Nano Technology, University of Kashan, Kashan P. O. Box. 87317-51167, Islamic Republic of Iran Department of Chemistry, Kosar University of Bojnord, Bojnord, Islamic Republic of Iran
A R T I C L E I N F O
Article history: Received 22 October 2013 Accepted 17 December 2013 Available online xxx Keywords: Nanoparticle Sonochemical synthesis HgSe Hydrazine KBH4
A B S T R A C T
A convenient sonochemical process for the preparation of mercury selenide (HgSe) nanoparticles has been developed based on the reaction of mercury salt and SeCl4 in the presence of triethanolamine (TEA) as complexing agent and N2H4H2O (hydrazine hydrate) as the reductant agent at room temperature. The effects of preparation parameters such as metal salt, reaction time, reductant agent and its quantity on the morphology, the particle size and the phase of the final products have been investigated. The products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray powder diffraction (XRD). ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction Nanocrystalline chalcogenides of the late transition metals have attracted a great deal of attention because of their unique thermoelectric, semiconducting and optical properties. Most studies in this area have been focused on cadmium and zinc compounds [1–3] and only a few publications report on the synthesis of mercury chalcogenides, mostly due to the high toxicity of mercury. Nevertheless, mercury chalcogenides are promising materials for catalysts, infrared detectors [4], light emitting diodes and electrochemical cells [5,6]. In particular, nanocrystalline HgSe is one of the candidate materials in IR detectors, IR emitters and tunable lasers [7]. The electrical properties of HgSe lead to the wide applications in optoelectronic technology including photoconductive photovoltaic, IR detector, IR emitter, tunable lasers and thermoelectric coolers [8,9]. HgSe has a unique combination of properties; it is a semimetal, characterized by high electron mobility, large electron concentration and a variation of band gap with temperature [10]. In this work, a simple and quick sonochemical method is employed to prepare HgSe nanoparticles. The ultrasound irradiation method has advantages such as rapid reaction rate, controllable reaction, uniform shape, narrow size distribution and high purity [11]. The chemical effects of ultrasound arise from
* Corresponding author. Tel.: +98 361 591 2383; fax: +98 361 555 2930. E-mail address: [email protected] (M. Salavati-Niasari).
the phenomenon called acoustic cavitation, i.e., the formation, growth and implosive collapse of bubbles in an ultrasonically irradiated liquid. The unique reaction conditions, temperatures of 5000 K, pressures of about 500 bar and rapid cooling rates greater than 109 K/s, enable the synthesis of metastable phases that are difficult to prepare in other ways [12]. For a few years, we have been interested in the synthesis of nanoparticles using this method [13–15]. Here, HgSe nanoparticles are prepared by using different mercury salts and SeCl4 in the presence of TEA and hydrazine. The effect of different synthetic conditions such as metal salt, reaction time, reductant agent and its quantity on the morphologies and size of the final products were investigated. 2. Experimental 2.1. Materials and physical measurements All the chemicals were of analytical grade and were used and received without further purification. A multiwave ultrasonic generator (Sonicator 3000; Bandeline, MS 72, Germany), equipped with a converter/transducer and titanium oscillator (horn), 12.5 mm in diameter, operating at 20 kHz with a maximum power output of 60 W, was used for the ultrasonic irradiation. The ultrasonic generator automatically adjusted the power level. The wave amplitude in each experiment was adjusted as needed. XRD of products was recorded by a Rigaku D-max C III XRD using Nifiltered Cu Ka radiation. SEM images were obtained on Philips
1226-086X/$ – see front matter ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2013.12.044
Please cite this article in press as: M. Esmaeili-Zare, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2013.12.044
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Table 1 The reaction conditions of the samples synthesized in this work. Sample Effect
Precursor
Reductant N2H4H2O Ultrasound T time (min) (8C) (ml)
1 2 3 4
HgCl2 Hg(CH3COO)2 HgBr2 Hg(NO3)2
30 30 30 30
25 25 25 25
N2H4H2O N2H4H2O N2H4H2O N2H4H2O
HgCl2 HgCl2 HgCl2
15 45 60
25 25 25
N2H4H2O 2 N2H4H2O 2 N2H4H2O 2
Quantity of HgBr2 hydrazine HgBr2
30
25
N2H4H2O 3
30
25
N2H4H2O 4
30 30 30
25 96 25
Zn Zn KBH4
–
25
N2H4H2O 2
5 6 7 8 9
Precursor
Time
10 11 12
Reductant
HgBr2 HgBr2 HgBr2
13
Sonication
HgBr2
2 2 2 2
– – –
XL-30ESEM equipped with an energy dispersive X-ray spectroscopy. TEM image was obtained on a Philips EM208 transmission electron microscope with an accelerating voltage of 200 kV. The EDS analysis with 20 kV accelerated voltage was done. Room temperature PL was studied on a PerkinElmer (LS 55) fluorescence spectrophotometer. 2.2. Synthesis of HgSe nanoparticles An aqueous solution of mercury salt in the presence of TEA was mixed with SeCl4 aqueous solution. Then the solution was
Fig. 1. XRD patterns of HgSe nanoparticles obtained from SeCl4 and (a) HgCl2 (Sample No. 1); (b) Hg(OAc)2 (Sample No. 2); (c) HgBr2 (Sample No. 3).
irradiated with an ultrasonic horn and hydrazine was added drop-wise. The black precipitates obtained were centrifuged and washed by distilled water and ethanol in sequence and dried in vacuum at 80 8C.
Fig. 2. SEM images of HgSe obtained from SeCl4 and (a) HgCl2 (Sample No. 1); (b) Hg(OAc)2 (Sample No. 2); (c) HgBr2 (Sample No. 3); (d) Hg(NO3)2 (Sample No. 4) in the presence of TEA and hydrazine.
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Fig. 3. TEM picture of HgSe (Sample No. 3).
3. Results and discussion The mechanism of the sonochemical formation of HgSe is probably related to the radical species generated from water molecules by the absorption of the ultrasound energy [16–18]. The probable reaction mechanism can be explained as follows: SeCl4 þ 3H2 O ! H2 SeO3 þ 4HCl
(1)
½HgðTEAÞn 2þ ! Hg2þ þ nTEA
(2)
H2 O ! H þ OH
(3)
4H þ H2 SeO3 ! Se2 þ 3H2 O
(4)
Hg2þ þ N2 H4 þ 4OH ! HgðOHÞ2 þ N2 þ 2Hþ þ 2H2 O
(5)
HgðOHÞ2 þ Se2 ! HgSe þ 2OH
(6)
In this process, the in situ generated .H would react with H2SeO3 to form Se2 ions that rapidly combine with Hg(OH)2, obtained from Eq. (5), to give HgSe nuclei [11,19]. The effects of mercury salt, reaction time, reductant agent and its quantity on the morphology, the particle size and the phase of HgSe samples have been investigated. The results have been listed in Table 1. The phase purity and crystal structure of the as-obtained products were characterized by XRD analysis. Fig. 1 shows XRD patterns of the samples prepared using different mercury salts. The reflection peaks of patterns were recorded in the 2u range of 10 – 808. All of the peaks in the patterns can be indexed as cubic HgSe with calculated lattice parameters of a = b = c = 0.6072 nm, which agree well with the reported values for HgSe (JCPDS 73-1668). No peaks attributable to other phases or compounds were observed, indicating that a pure HgSe phase has been formed after the synthesis for all samples. The strong and sharp reflection peaks suggest that the as-synthesized products are well-crystallized. The morphology of the products was examined by SEM. Fig. 2 contains the SEM pictures of the HgSe prepared using SeCl4 and different mercury salts, in the presence of TEA and hydrazine after
Fig. 4. SEM images of HgSe obtained from HgCl2 in the presence of TEA after: (a) 15 min (Sample No. 5); (b) 45 min (Sample No. 6); (c) 60 min (Sample No. 7) of sonication.
30 min of sonification. From the micrographs, it is observed that the nano-sized samples are agglomerated. To reach an ideal morphology, we prepared nanosized HgSe using four mercury salts, such as HgCl2, Hg(OAc)2, HgBr2 and Hg(NO3)2). It shows that the utilization of HgCl2 declines the agglomeration of the nanosized samples and the growth of the particles. The morphology and size distribution of the products were further studied by TEM. A TEM photograph of the Sample No. 3 is given in Fig. 3. The TEM image shows the presence of dense
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agglomerates of nanoparticles. The diameters of these nanoparticles are 15–35 nm. In other side, the effect of reaction time on sonochemical method on the morphology and particle size of HgSe nanostructures was investigated. With increasing reaction time from 30 min (Fig. 2a) to 45 min (Fig. 4b) and then 60 min (Fig. 4c), the size and agglomeration of the nanoparticles increased. Fig. 5 shows SEM images of the HgSe nanoparticles prepared in the presence of different quantities of hydrazine. In the synthesis of cubic phase HgSe nanoparticles, our present experiments, quantity of hydrazine has a small influence on the morphology and particle size of products. In continues, the effect of the type of reductant on the morphology of HgSe nanostructures obtained from HgBr2 in the presence of TEA was investigated. In this study, three reducing agents were applied that including N2H4H2O, Zn and KBH4. SEM images in Fig. 6 show that the morphology and particle size, and therefore the properties, of the products can be affected by the type of reductant. In the presence of hydrazine in Sample No. 3 (Fig. 2c) nanoparticles are formed, it is observed that the nanoparticles are agglomerated. On changing hydrazine to Zn in Sample No. 10, particles are highly agglomerated (Fig. 6a). Meanwhile, in the presence of KBH4 in Sample No. 12, size and agglomeration of the nanoparticles is decreased (Fig. 6c). Fig. 6b shows that with increasing temperature from 25 8C (Sample No. 10) to 96 8C (Sample No. 11) in the presence of Zn, the morphology of asprepared product is change from semi-spherical nanoparticles to flower-like nanostructures. The XRD pattern of Sample No. 10 is shown in Fig. 6d. All peaks in the pattern correspond to the reflections of HgSe (JCPDS 75-1554). Fairly monodispersed small particles are produced by hydroboration such as the sodium borohydrides (NaBH4) and potassium borohydrides (KBH4). The adsorption of BH4nucleophile onto the surface of products will increase its Fermi potential, thus reducing its reduction potential. The strong reductant KBH4 and N2H4 in combination with stirring rapidly create a large number of nuclei and further growth of the nuclei is limited. As a result, many small particles are obtained. The reduction in the presence of Zn proceeds only two-dimensionally, i.e., at the interface of Zn powder with the metal cation solution. The rate of reduction is further limited by the mass transport of the metal cation solution to the Zn surface. Therefore, depletion of metal cations near the interface might occur. As a consequence of the
rate and surface area limitation, crystal growth is favored over nucleus formation as the result of larger particles [20]. For investigating the effect of sonication on the morphology and particle size of the products, the reaction carried out in the absence of sonication (Fig. 7). It is clear that aggregated nanostructures are formed in the absence of sonocation. As a result, the expected products could not be obtained under mechanical stirring conditions. It is indicated that ultrasoundassisted method is a convenient and quick approach to prepare HgSe nanoparticles. The optical properties of the HgSe samples were characterized by the PL spectrum. The room temperature PL spectrum of the HgSe (Sample No. 3) was recorded in ethanol solution (Fig. 8). The sample kept at room temperature was excited with excitation wavelength 260 nm. The emission spectrum in 384 nm shows a deviation from a Gaussian curve confirming the uneven distribution of particles. The determined band gap of this sample is 3.23 eV, while that of bulk HgSe is 0.24 eV [21]. The Sample No. 3 shows a blue-shifted emission compared to bulk sample. This further confirms the larger variation of particle sizes. The band gaps increase with the decreasing of the particle sizes [22]. EDS analysis was employed to investigate the chemical composition and purity of as-synthesized HgSe nanoparticles. The results for HgSe in the presence of TEA and hydrazine for 30 min of sonification (Sample No. 3) show that there exist only the elements Hg and Se (Fig. 9), which indicates the pure HgSe phase in the nanoparticles. In addition, neither N, O nor C signals were detected in the EDS spectrum, which means no complexing agent exists in the nanoparticles. The choice of synthesis method, the type of metal and selenide source, the reductant agent and its quantity, the reaction time, etc., are key factors in the preparation of metal selenides. The methods used in the present study are simple and have low cost and can be scaled-up. With this route, we have used non-toxic precursors and solvent and applied SeCl4 and various reductant types, which are rare in the preparation of HgSe nanoparticles. The SeCl4 is a good Se source, which well dissolves in distilled water and homogeneously releases Se2 in the presence of reductant [23,24]. We have chosen SeCl4 as the Se source to synthesize mercury selenides and found the application of SeCl4 can affect the size of HgSe. To the best of our knowledge, it is the first time that SeCl4 has been used as the Se source for the synthesis of HgSe nanoparticles by sonochemical method.
Fig. 5. SEM images of HgSe obtained from HgBr2 in the presence of (a) 3 ml (Sample No. 8); (b) 4 ml (Sample No. 9) of hydrazine.
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Fig. 7. SEM image of Sample No. 13.
Fig. 8. PL spectrum of HgSe (Sample No. 3).
Fig. 6. SEM images of HgSe obtained from HgBr2 in the presence of: (a) Zn (T = 25 8C) (Sample No. 10); (b) Zn (T = 96 8C) (Sample No. 11); (c) KBH4 (Sample No. 12); (d) XRD pattern of Sample No. 10.
Fig. 9. EDS pattern of HgSe (Sample No. 3).
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4. Conclusion In this work, a simple and quick sonochemical method was employed to prepare HgSe nanoparticles, by using SeCl4 and different mercury salts in the presence of TEA as complexing agent and hydrazine, Zn and KBH4 as the reductant agents. The effects of preparation parameters such as metal salt, reaction time, reductant agent and its quantity on the morphology, the particle size and the phase of the final products were investigated. This route may be extended to the fabrication of other metal selenides with novel morphologies and properties. Acknowledgment Authors are grateful to Council of Institute of Nano Science and Nano Technology, University of Kashan and for providing financial support to undertake work by Grant No. (159271/133). References [1] M. Salavati-Niasari, M. Esmaeili-Zare, A. Sobhani, Micro Nano Lett. 7 (2012) 831– 834. [2] K. Sooklal, B.S. Cullum, S.M. Angel, C.J. Murphy, J. Phys. Chem. 100 (1996) 4551– 4555. [3] M. Fromment, H. Cachet, H. Essaaidi, G. Maurin, R. Cortes, Pure Appl. Chem. 69 (1997) 77–82. [4] G. Debias, Phys. Status Solidi A 83 (1984) 269–278.
[5] V.L. Colvin, M.C. Schlamp, A.P. Aliviastors, Nature 370 (1994) 354–357. [6] A. Hangfeldt, M. Gratzel, Chem. Rev. 95 (1995) 49–68. [7] M.K. Mathe, S.M. Cox, V. Venkatasamy, U. Happek, J.L. Stickney, J. Electrochem. Soc. 152 (2005) C751–C755. [8] R.K. Willardson, A.C. Beer, Semiconductors and Semimetals, 16, Academic Press, New York, 1981. [9] K. Singh, S.S.D. Mishra, J. Ind. Chem. Soc. 76 (1999) 104–106. [10] J. Ren, D.B. Eason, L.E. Churchill, Z. Yu, C. Boney, J.W. Cook, J.F. Schetzina, N.A. ElMasry, J. Cryst. Growth 138 (1994) 455–463. [11] H. Wang, S. Xu, X.N. Zhao, J.J. Zhu, X.Q. Xin, Mater. Sci. Eng. B 96 (2002) 60–64. [12] K.S. Suslick, Science 247 (1990) 1439–1445. [13] M. Salavati-Niasari, G. Hosseinzadeh, F. Davara, J. Alloy. Compd. 509 (2011) 134– 140. [14] M. Esmaeili-Zare, M. Salavati-Niasari, A. Sobhani, Ultrason. Sonochem. 19 (2012) 1079–1086. [15] M. Salavati-Niasari, J. Javidi, F. Davar, A. Amini Fazl, J. Alloy. Compd. 503 (2010) 500–506. [16] H.L. Li, Y.C. Zhu, S.G. Chen, O. Palchik, J.P. Xiong, Y. Koltyipin, Y. Gofer, A. Gedanken, J. Solid State Chem. 172 (2003) 102–110. [17] G.Z. Wang, W. Chen, C.H. Liang, Y.W. Wang, G.W. Meng, L.D. Zhang, Inorg. Chem. Commun. 4 (2001) 208–210. [18] M. Behboudnia, Y. Azizianekalandaragh, Mater. Sci. Eng. B 138 (2007) 65–68. [19] J. Geng, B. Liu, L. Xu, F.N. Hu, J.J. Zhu, Langmuir 23 (2007) 10286–10293. [20] A. Trifonova, M. Wachtler, M.R. Wagner, H. Schroettner, Ch. Mitterbauer, F. Hofer, K.C. Moller, M. Winter, J.O. Besenhard, Solid State Ionics 168 (2004) 51–59. [21] C.Y. Moon, S.H. Wei, Phys. Rev. B 74 (2006) 045205–045209. [22] A. Cortes, H. Gomez, R.E. Marotti, G. Riveros, E.A. Dalchiele, Sol. Energy Mater. Sol. Cells 82 (2004) 21–34. [23] M. Esmaeili-Zare, M. Salavati-Niasari, D. Ghanbari, High Temp. Mater. Process. 32 (2013) 157–162. [24] M. Salavati-Niasari, M. Esmaeili-Zare, A. Sobhani, Micro Nano Lett. 7 (2012) 1300– 1304.
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JIEC-1774; No. of Pages 6 Journal of Industrial and Engineering Chemistry xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Journal of Industrial and Engineering Chemistry journal homepage: www.elsevier.com/locate/jiec
Sonochemical synthesis of HgSe nanoparticles: Effect of metal salt, reaction time and reductant agent Mahdiyeh Esmaeili-Zare a, Masoud Salavati-Niasari a,*, Azam Sobhani b a b
Institute of Nano Science and Nano Technology, University of Kashan, Kashan P. O. Box. 87317-51167, Islamic Republic of Iran Department of Chemistry, Kosar University of Bojnord, Bojnord, Islamic Republic of Iran
A R T I C L E I N F O
Article history: Received 22 October 2013 Accepted 17 December 2013 Available online xxx Keywords: Nanoparticle Sonochemical synthesis HgSe Hydrazine KBH4
A B S T R A C T
A convenient sonochemical process for the preparation of mercury selenide (HgSe) nanoparticles has been developed based on the reaction of mercury salt and SeCl4 in the presence of triethanolamine (TEA) as complexing agent and N2H4H2O (hydrazine hydrate) as the reductant agent at room temperature. The effects of preparation parameters such as metal salt, reaction time, reductant agent and its quantity on the morphology, the particle size and the phase of the final products have been investigated. The products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray powder diffraction (XRD). ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.
1. Introduction Nanocrystalline chalcogenides of the late transition metals have attracted a great deal of attention because of their unique thermoelectric, semiconducting and optical properties. Most studies in this area have been focused on cadmium and zinc compounds [1–3] and only a few publications report on the synthesis of mercury chalcogenides, mostly due to the high toxicity of mercury. Nevertheless, mercury chalcogenides are promising materials for catalysts, infrared detectors [4], light emitting diodes and electrochemical cells [5,6]. In particular, nanocrystalline HgSe is one of the candidate materials in IR detectors, IR emitters and tunable lasers [7]. The electrical properties of HgSe lead to the wide applications in optoelectronic technology including photoconductive photovoltaic, IR detector, IR emitter, tunable lasers and thermoelectric coolers [8,9]. HgSe has a unique combination of properties; it is a semimetal, characterized by high electron mobility, large electron concentration and a variation of band gap with temperature [10]. In this work, a simple and quick sonochemical method is employed to prepare HgSe nanoparticles. The ultrasound irradiation method has advantages such as rapid reaction rate, controllable reaction, uniform shape, narrow size distribution and high purity [11]. The chemical effects of ultrasound arise from
* Corresponding author. Tel.: +98 361 591 2383; fax: +98 361 555 2930. E-mail address: [email protected] (M. Salavati-Niasari).
the phenomenon called acoustic cavitation, i.e., the formation, growth and implosive collapse of bubbles in an ultrasonically irradiated liquid. The unique reaction conditions, temperatures of 5000 K, pressures of about 500 bar and rapid cooling rates greater than 109 K/s, enable the synthesis of metastable phases that are difficult to prepare in other ways [12]. For a few years, we have been interested in the synthesis of nanoparticles using this method [13–15]. Here, HgSe nanoparticles are prepared by using different mercury salts and SeCl4 in the presence of TEA and hydrazine. The effect of different synthetic conditions such as metal salt, reaction time, reductant agent and its quantity on the morphologies and size of the final products were investigated. 2. Experimental 2.1. Materials and physical measurements All the chemicals were of analytical grade and were used and received without further purification. A multiwave ultrasonic generator (Sonicator 3000; Bandeline, MS 72, Germany), equipped with a converter/transducer and titanium oscillator (horn), 12.5 mm in diameter, operating at 20 kHz with a maximum power output of 60 W, was used for the ultrasonic irradiation. The ultrasonic generator automatically adjusted the power level. The wave amplitude in each experiment was adjusted as needed. XRD of products was recorded by a Rigaku D-max C III XRD using Nifiltered Cu Ka radiation. SEM images were obtained on Philips
1226-086X/$ – see front matter ß 2013 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jiec.2013.12.044
Please cite this article in press as: M. Esmaeili-Zare, et al., J. Ind. Eng. Chem. (2014), http://dx.doi.org/10.1016/j.jiec.2013.12.044
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Table 1 The reaction conditions of the samples synthesized in this work. Sample Effect
Precursor
Reductant N2H4H2O Ultrasound T time (min) (8C) (ml)
1 2 3 4
HgCl2 Hg(CH3COO)2 HgBr2 Hg(NO3)2
30 30 30 30
25 25 25 25
N2H4H2O N2H4H2O N2H4H2O N2H4H2O
HgCl2 HgCl2 HgCl2
15 45 60
25 25 25
N2H4H2O 2 N2H4H2O 2 N2H4H2O 2
Quantity of HgBr2 hydrazine HgBr2
30
25
N2H4H2O 3
30
25
N2H4H2O 4
30 30 30
25 96 25
Zn Zn KBH4
–
25
N2H4H2O 2
5 6 7 8 9
Precursor
Time
10 11 12
Reductant
HgBr2 HgBr2 HgBr2
13
Sonication
HgBr2
2 2 2 2
– – –
XL-30ESEM equipped with an energy dispersive X-ray spectroscopy. TEM image was obtained on a Philips EM208 transmission electron microscope with an accelerating voltage of 200 kV. The EDS analysis with 20 kV accelerated voltage was done. Room temperature PL was studied on a PerkinElmer (LS 55) fluorescence spectrophotometer. 2.2. Synthesis of HgSe nanoparticles An aqueous solution of mercury salt in the presence of TEA was mixed with SeCl4 aqueous solution. Then the solution was
Fig. 1. XRD patterns of HgSe nanoparticles obtained from SeCl4 and (a) HgCl2 (Sample No. 1); (b) Hg(OAc)2 (Sample No. 2); (c) HgBr2 (Sample No. 3).
irradiated with an ultrasonic horn and hydrazine was added drop-wise. The black precipitates obtained were centrifuged and washed by distilled water and ethanol in sequence and dried in vacuum at 80 8C.
Fig. 2. SEM images of HgSe obtained from SeCl4 and (a) HgCl2 (Sample No. 1); (b) Hg(OAc)2 (Sample No. 2); (c) HgBr2 (Sample No. 3); (d) Hg(NO3)2 (Sample No. 4) in the presence of TEA and hydrazine.
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Fig. 3. TEM picture of HgSe (Sample No. 3).
3. Results and discussion The mechanism of the sonochemical formation of HgSe is probably related to the radical species generated from water molecules by the absorption of the ultrasound energy [16–18]. The probable reaction mechanism can be explained as follows: SeCl4 þ 3H2 O ! H2 SeO3 þ 4HCl
(1)
½HgðTEAÞn 2þ ! Hg2þ þ nTEA
(2)
H2 O ! H þ OH
(3)
4H þ H2 SeO3 ! Se2 þ 3H2 O
(4)
Hg2þ þ N2 H4 þ 4OH ! HgðOHÞ2 þ N2 þ 2Hþ þ 2H2 O
(5)
HgðOHÞ2 þ Se2 ! HgSe þ 2OH
(6)
In this process, the in situ generated .H would react with H2SeO3 to form Se2 ions that rapidly combine with Hg(OH)2, obtained from Eq. (5), to give HgSe nuclei [11,19]. The effects of mercury salt, reaction time, reductant agent and its quantity on the morphology, the particle size and the phase of HgSe samples have been investigated. The results have been listed in Table 1. The phase purity and crystal structure of the as-obtained products were characterized by XRD analysis. Fig. 1 shows XRD patterns of the samples prepared using different mercury salts. The reflection peaks of patterns were recorded in the 2u range of 10 – 808. All of the peaks in the patterns can be indexed as cubic HgSe with calculated lattice parameters of a = b = c = 0.6072 nm, which agree well with the reported values for HgSe (JCPDS 73-1668). No peaks attributable to other phases or compounds were observed, indicating that a pure HgSe phase has been formed after the synthesis for all samples. The strong and sharp reflection peaks suggest that the as-synthesized products are well-crystallized. The morphology of the products was examined by SEM. Fig. 2 contains the SEM pictures of the HgSe prepared using SeCl4 and different mercury salts, in the presence of TEA and hydrazine after
Fig. 4. SEM images of HgSe obtained from HgCl2 in the presence of TEA after: (a) 15 min (Sample No. 5); (b) 45 min (Sample No. 6); (c) 60 min (Sample No. 7) of sonication.
30 min of sonification. From the micrographs, it is observed that the nano-sized samples are agglomerated. To reach an ideal morphology, we prepared nanosized HgSe using four mercury salts, such as HgCl2, Hg(OAc)2, HgBr2 and Hg(NO3)2). It shows that the utilization of HgCl2 declines the agglomeration of the nanosized samples and the growth of the particles. The morphology and size distribution of the products were further studied by TEM. A TEM photograph of the Sample No. 3 is given in Fig. 3. The TEM image shows the presence of dense
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agglomerates of nanoparticles. The diameters of these nanoparticles are 15–35 nm. In other side, the effect of reaction time on sonochemical method on the morphology and particle size of HgSe nanostructures was investigated. With increasing reaction time from 30 min (Fig. 2a) to 45 min (Fig. 4b) and then 60 min (Fig. 4c), the size and agglomeration of the nanoparticles increased. Fig. 5 shows SEM images of the HgSe nanoparticles prepared in the presence of different quantities of hydrazine. In the synthesis of cubic phase HgSe nanoparticles, our present experiments, quantity of hydrazine has a small influence on the morphology and particle size of products. In continues, the effect of the type of reductant on the morphology of HgSe nanostructures obtained from HgBr2 in the presence of TEA was investigated. In this study, three reducing agents were applied that including N2H4H2O, Zn and KBH4. SEM images in Fig. 6 show that the morphology and particle size, and therefore the properties, of the products can be affected by the type of reductant. In the presence of hydrazine in Sample No. 3 (Fig. 2c) nanoparticles are formed, it is observed that the nanoparticles are agglomerated. On changing hydrazine to Zn in Sample No. 10, particles are highly agglomerated (Fig. 6a). Meanwhile, in the presence of KBH4 in Sample No. 12, size and agglomeration of the nanoparticles is decreased (Fig. 6c). Fig. 6b shows that with increasing temperature from 25 8C (Sample No. 10) to 96 8C (Sample No. 11) in the presence of Zn, the morphology of asprepared product is change from semi-spherical nanoparticles to flower-like nanostructures. The XRD pattern of Sample No. 10 is shown in Fig. 6d. All peaks in the pattern correspond to the reflections of HgSe (JCPDS 75-1554). Fairly monodispersed small particles are produced by hydroboration such as the sodium borohydrides (NaBH4) and potassium borohydrides (KBH4). The adsorption of BH4nucleophile onto the surface of products will increase its Fermi potential, thus reducing its reduction potential. The strong reductant KBH4 and N2H4 in combination with stirring rapidly create a large number of nuclei and further growth of the nuclei is limited. As a result, many small particles are obtained. The reduction in the presence of Zn proceeds only two-dimensionally, i.e., at the interface of Zn powder with the metal cation solution. The rate of reduction is further limited by the mass transport of the metal cation solution to the Zn surface. Therefore, depletion of metal cations near the interface might occur. As a consequence of the
rate and surface area limitation, crystal growth is favored over nucleus formation as the result of larger particles [20]. For investigating the effect of sonication on the morphology and particle size of the products, the reaction carried out in the absence of sonication (Fig. 7). It is clear that aggregated nanostructures are formed in the absence of sonocation. As a result, the expected products could not be obtained under mechanical stirring conditions. It is indicated that ultrasoundassisted method is a convenient and quick approach to prepare HgSe nanoparticles. The optical properties of the HgSe samples were characterized by the PL spectrum. The room temperature PL spectrum of the HgSe (Sample No. 3) was recorded in ethanol solution (Fig. 8). The sample kept at room temperature was excited with excitation wavelength 260 nm. The emission spectrum in 384 nm shows a deviation from a Gaussian curve confirming the uneven distribution of particles. The determined band gap of this sample is 3.23 eV, while that of bulk HgSe is 0.24 eV [21]. The Sample No. 3 shows a blue-shifted emission compared to bulk sample. This further confirms the larger variation of particle sizes. The band gaps increase with the decreasing of the particle sizes [22]. EDS analysis was employed to investigate the chemical composition and purity of as-synthesized HgSe nanoparticles. The results for HgSe in the presence of TEA and hydrazine for 30 min of sonification (Sample No. 3) show that there exist only the elements Hg and Se (Fig. 9), which indicates the pure HgSe phase in the nanoparticles. In addition, neither N, O nor C signals were detected in the EDS spectrum, which means no complexing agent exists in the nanoparticles. The choice of synthesis method, the type of metal and selenide source, the reductant agent and its quantity, the reaction time, etc., are key factors in the preparation of metal selenides. The methods used in the present study are simple and have low cost and can be scaled-up. With this route, we have used non-toxic precursors and solvent and applied SeCl4 and various reductant types, which are rare in the preparation of HgSe nanoparticles. The SeCl4 is a good Se source, which well dissolves in distilled water and homogeneously releases Se2 in the presence of reductant [23,24]. We have chosen SeCl4 as the Se source to synthesize mercury selenides and found the application of SeCl4 can affect the size of HgSe. To the best of our knowledge, it is the first time that SeCl4 has been used as the Se source for the synthesis of HgSe nanoparticles by sonochemical method.
Fig. 5. SEM images of HgSe obtained from HgBr2 in the presence of (a) 3 ml (Sample No. 8); (b) 4 ml (Sample No. 9) of hydrazine.
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Fig. 7. SEM image of Sample No. 13.
Fig. 8. PL spectrum of HgSe (Sample No. 3).
Fig. 6. SEM images of HgSe obtained from HgBr2 in the presence of: (a) Zn (T = 25 8C) (Sample No. 10); (b) Zn (T = 96 8C) (Sample No. 11); (c) KBH4 (Sample No. 12); (d) XRD pattern of Sample No. 10.
Fig. 9. EDS pattern of HgSe (Sample No. 3).
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4. Conclusion In this work, a simple and quick sonochemical method was employed to prepare HgSe nanoparticles, by using SeCl4 and different mercury salts in the presence of TEA as complexing agent and hydrazine, Zn and KBH4 as the reductant agents. The effects of preparation parameters such as metal salt, reaction time, reductant agent and its quantity on the morphology, the particle size and the phase of the final products were investigated. This route may be extended to the fabrication of other metal selenides with novel morphologies and properties. Acknowledgment Authors are grateful to Council of Institute of Nano Science and Nano Technology, University of Kashan and for providing financial support to undertake work by Grant No. (159271/133). References [1] M. Salavati-Niasari, M. Esmaeili-Zare, A. Sobhani, Micro Nano Lett. 7 (2012) 831– 834. [2] K. Sooklal, B.S. Cullum, S.M. Angel, C.J. Murphy, J. Phys. Chem. 100 (1996) 4551– 4555. [3] M. Fromment, H. Cachet, H. Essaaidi, G. Maurin, R. Cortes, Pure Appl. Chem. 69 (1997) 77–82. [4] G. Debias, Phys. Status Solidi A 83 (1984) 269–278.
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